Having excellent characteristics such as a high energy density and a high cell voltage, lithium ion batteries are widely used mainly for electronic equipment such as cellular phones, portable video cameras and notebook personal computers. Batteries used for such electronic equipment are often commercially available in the form of a battery pack having the number of single cells as required accommodated in a case made of resin, considering safety, ease of use, a required voltage and the like.
In secondary batteries such as lithium ion batteries, charge/discharge is repeated on the order of several hundred times, leading to deterioration of an electrode, an electrolytic solution or the like. This causes reduction in a quantity of chargeable electricity. Such batteries are regarded as reaching their end of life and discarded as waste batteries. Here, valuables including rare metals such as cobalt and nickel are used for lithium ion batteries, and therefore, a process for disassembling cells, collecting valuable metals and recycling them is performed.
Batteries are generally recycled by crushing the cells, followed by concentrating valuable metals with using various methods.
However, if non-discharge cells are included at the time of crushing cells, heat may be generated due to a short circuit resulting from crushing the cells. This may cause an organic solvent included in an electrolyte in the cell to volatilize, thereby jetting gas. In some cases, the cell may burst into flame when exceeding an ignition point. In particular, such heat generation or explosion significantly occurs in lithium ion battery cells having a high voltage, leading to danger.
Various methods for safely crushing cells have been proposed in order to solve such a problem. As an example, disclosed is a method for suppressing an influence of heat generation or ignition by throwing cells, as they are, into a furnace with a high temperature regardless of a state of charge/discharge, followed by firing the cells (for example, Patent Literature 1). As another example, disclosed is a method for immersing cells in a liquid having conductivity (hereinafter, referred to as a discharge liquid), causing the cells to discharge, and then, crushing the cells (for example, Patent Literature 2).
As for the method for performing the firing process, there is a problem that lead is scattered because a circuit board is included in the battery pack. There is also a problem that an exhaust gas treatment facility is required because a case made of resin is decomposed to emit a nitrogen compound.
As for the method for discharging cells by immersing the cells in the discharge liquid, it takes relatively a short time, on the order of several hours to 24 hours, to discharge single cells in the case of immersing the single cells individually in the discharge liquid. On the other hand, when the battery pack is immersed in the discharge liquid, it takes on the order of several times to 10 times as long as the case of immersing the single cells individually. This is because the battery pack includes a protection circuit for preventing an over-discharge. Even if the battery pack is immersed in the discharge liquid, the protection circuit suppresses a discharge current.
As described above, it disadvantageously takes longtime to discharge the battery pack, costing much labor during the operation and much money.